Question

The occurrence of casting defect "rat tail" is possible because of: A. soft ramming of sand
B. continuous large flat surface on the mould
C. excessive hardness of the mould
D. hard ramming of sand

• A. A and B only
• B. B and C only
• C. A and C only
• D. B and D only

Hint:

Rat tail defect = thermal expansion + restraint (hard ramming + large flat surfaces).

Answer 1

The Correct Option is D

Concept: Rat tail is a casting defect caused due to thermal expansion of mould surface leading to buckling of sand.

Step 1: Understand the mechanism.
When molten metal is poured:
• Surface of mould heats up rapidly
• Sand expands
• If expansion is restrained → buckling occurs → forms rat tail defect

Step 2: Evaluate option A (Soft ramming).
Soft ramming:
• Allows expansion easily
• Reduces stress buildup Hence does NOT cause defect → false.

Step 3: Evaluate option B (Large flat surface).
Large flat surfaces:
• Provide long expansion path
• Increase tendency of buckling Hence true.

Step 4: Evaluate option C (Excessive hardness).
Hardness increases strength but not main cause of rat tail:
• Rat tail mainly due to thermal expansion constraint Hence not primary → false.

Step 5: Evaluate option D (Hard ramming).
Hard ramming:
• Restricts sand expansion
• Causes compressive stress → buckling Hence true.

Step 6: Final conclusion.
Correct causes: \[ B \text{ and } D \] \[ \boxed{\text{Answer: B and D only}} \]